GIT Physicochemical Modeling - A Critical Review

Many attempts to model the human gastrointestinal tract (GIT) were made since the beginning of the last decade. The main purpose was either to simulate an in vivo testing of drugs on animals or to investigate the viability of the probiotic intake. Two well-known physio-chemical models regarding the viability of the probiotics have been produced. In 1993, Molly et al. developed a simulator of the human intestinal microbial ecosystem (SHIME). Six reactors simulating the conditions of human stomach, duodenum/jejunum, ileum, caecum/ascending colon, transverse colon and descending colon were artificially developed. In 1995, Minekus et al. created a TNO gastro-intestinal model (TIM) with four computer-controlled chambers simulating the conditions of stomach, duodenum, jejunum and ileum. The simulated parameters included the body temperature, pH, salivary, gastric and intestinal mixing with peristaltic movements, secretions and absorption of water and small molecules. Despite the use of pharmacological, physiological and biochemical knowledge of the human and animal GIT and associated secretions, conflicting results such as the extremely low viability of probiotics were obtained. The failure of the above two models indicates the necessity of devising a suitable in vitro model that would be capable of simulating the digestion process as an exact replica of the actual in vivo model. In this paper, the key aspects of the above have been summarized and discussed.